In a prescribed space of control of a building structure, a mechanical apparatus, etc., a slit fluid jet has hitherto been used as means for preventing fluid and solid from entering into the space of control from outside, or for preventing fluid and solid from escaping from the space of control to the outside.
For example, in a general type of building structure, an air curtain that is a kind of slit fluid jet is ejected at each of the inlet and outlet thereof to thereby make effective the zoning between the space of control and the external air, thereby the air-conditioning efficiency is successfully enhanced.
Also, in a processing apparatus for frozen food, air curtains are ejected from the surroundings of a processing part thereof, to thereby form a space of cool air for the low-temperature preservation of foodstuff.
Further, in a machine tool, liquid curtains or shower curtains are ejected from the surroundings of a machining part thereof, to thereby prevent cut shavings from being scattered, or splashing out, from the space of machining. This slit fluid jet such as the air curtain, liquid curtain, or shower curtain is formed by ejecting fluid from an apparatus using a pair of smooth flat surfaces or curved surfaces or an apparatus wherein nozzles are arrayed. 
However, although the above-described slit fluid jet has greatly contributed to forming the space of control, it has a lot of problems from the viewpoint of efficiently forming a large space of control.
Namely, to form a large space of control through the use of such a slit fluid jet, it is necessary to increase the velocity of that slit fluid jet. However, generally, increasing the velocity of the fluid results in the instability of the film of the fluid increasing. This raises the problem that the filmy fluid of the slit fluid jet is likely to be broken.
This likeliness to break of the fluid film of the slit fluid jet is attributable to the turbulence component (variable speed component) of the fluid. This turbulence component causes the exfoliation of the shearing layer on the inner wall of the slit, the creation of the exfoliation vortexes, the entrapment of air at the outlet of the slit, etc. It thereby makes the thickness of the fluid film of the slit fluid jet uneven, with the result that the fluid film becomes broken due even to a small intensity of disturbance.
On this account, as one of the countermeasures against this, it is thought to be possible to decrease the velocity of the slit fluid jet to thereby stabilize the film of the fluid. However, making the velocity of the fluid low results in that the fluid film is broken even by a small intensity of disturbance.
Also, further, the above-described likeliness of breaking the fluid film becomes serious as the distance as measured from the slit opening increases. Namely, as the distance from the slit opening increases, the thickness of the slit fluid jet becomes very small, so that it is easily broken due even to a very small magnitude of disturbance.
In order to take measures to address the problem of the above-described likeliness to break the fluid film, usually, in general, the fluid film of the slit fluid jet is made thick. However, this means increasing the flow rate of the slit fluid jet, but this becomes a factor causing a rise in the running cost.
Whereupon, this invention has been made in view of the shortcomings of the conventional techniques mentioned above, and an object of the present invention is to  provide a method of stabilizing a slit fluid jet and a device therefor which enable a stable fluid film to be formed from an ejection opening of the slit over a long distance with the slit fluid jet not being broken.